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Elk Creek is the first methane-to-energy project at a coal mine west of the Mississippi and the largest of its kind nationwide. (Aspen Skiing Company)

Squeezing Cleaner Energy from Coal’s Waste

Coal mine methane could soon transform from problematic waste to valuable fuel

smithsonian.com

In a Colorado valley where miners have harvested coal for more than a century, a second fuel—methane—escapes from the thick black seams of the Elk Creek mine. A system of boreholes and pipes around the mine funnels methane-rich gas to a modified truck engine. Using a trio of one-megawatt generators, the engine converts this methane to electricity for the local power grid.

Elk Creek is the first methane-to-energy project at a coal mine west of the Mississippi and the largest of its kind nationwide. But coal mines like Elk Creek contribute about 10 percent of methane emissions nationally and 6 percent of methane emissions worldwide, and they continue to release methane long after mining operations have ended. The gas also seeps from swamps, industrial flues, landfills, cattle farms and natural gas operations.

In fact, so much methane enters Earth’s atmosphere each year that globally it is the second largest contributor to climate change after carbon dioxide. Methane dissipates more quickly than carbon, but its strength as a greenhouse gas over a 100-year period is more than 20 times that of CO2.

Burning methane can generate energy or useful heat while lessening its climate impact—essentially reducing the gas to a weaker brew of water and carbon dioxide. At Elk Creek, burning just over 670,ooo cubic feet of methane per day—roughly 16 percent of the mine’s total methane emissions—in an internal combustion engine is expected to generate 24 gigawatt hours annually. That’s enough electricity to power roughly 2,000 homes.

By stopping methane from entering the atmosphere, the project will prevent emissions equivalent to more than 96,500 metric tons of CO2 annually over the next 15 years, according to estimates from its main funder, Aspen Skiing Company. That is about 10 days’ worth of carbon emissions from a typical coal-fired power plant—not enough to make a meaningful dent in global emissions of greenhouse gases, but an important step toward transforming methane from a problematic waste to a valuable fuel.

A combination of policy changes, creative new partnerships and technology innovation now means Elk Creek could be leading a much larger wave of similar projects harvesting methane from coal mines.

The Challenge

Historically, the owners of mines like Elk Creek in the U.S. have had little incentive to make use of methane. The gas sells for such low prices these days relative to other fuels that it would take many years to recoup the cost of installing the systems necessary to harvest it. As a result, mine owners simply allow the gas to enter the earth’s atmosphere.

And until recently, technology has limited mine operators to harnessing energy only from coal mine emissions with relatively high concentrations of methane. At concentrations above 80 percent, methane can be injected into natural gas pipelines or converted into liquefied natural gas for vehicles. At concentrations around 20 to 40 percent, the gas can fuel power generation as it does at Elk Creek, or industrial boilers that generate steam or hot water. According to a United Nations' report, most medium- and high-quality methane is used to generate either power or a combination of power and useful heat. This methane is typically collected into boreholes drilled around the site before actual mining begins.

Much of the methane coming out of coal mine shafts, however, is in low concentrations, mixed together with nitrogen, oxygen and other contaminants. This is because operators typically use ventilation systems to dilute any methane leaking into mine shafts with fresh air for worker safety: at 5 to 15 percent concentration in air, methane is explosive, and concentrations below 1 percent are required for healthy breathing.

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